Electromechanical system having a controlled atmosphere, and method of fabricating same

ABSTRACT

There are many inventions described and illustrated herein. In one aspect, the present invention is directed to a technique of fabricating or manufacturing MEMS having mechanical structures that operate in controlled or predetermined mechanical damping environments. In this regard, the present invention encapsulates the mechanical structures within a chamber, prior to final packaging and/or completion of the MEMS. The environment within the chamber containing and/or housing the mechanical structures provides the predetermined, desired and/or selected mechanical damping. The parameters of the encapsulated fluid (for example, the gas pressure) in which the mechanical structures are to operate are controlled, selected and/or designed to provide a desired and/or predetermined operating environment.

BACKGROUND

[0001] This invention relates to electromechanical systems andtechniques for fabricating microelectromechanical andnanoelectromechanical systems; and more particularly, in one aspect, tofabricating or manufacturing microelectromechanical andnanoelectromechanical systems having microstructures encapsulated in arelatively stable, controlled pressure environment to provide, forexample, a predetermined, desired and/or selected mechanical damping ofthe microstructure.

[0002] Microelectromechanical systems (“MEMS”), for example, gyroscopes,resonators and accelerometers, utilize micromachining techniques (i.e.,lithographic and other precision fabrication techniques) to reducemechanical components to a scale that is generally comparable tomicroelectronics. MEMS typically include a mechanical structurefabricated from or on, for example, a silicon substrate usingmicromachining techniques.

[0003] In order to protect the delicate mechanical structure, MEMS aretypically packaged in, for example, a hermetically sealed metalcontainer (for example, a TO-8 “can”, see, for example, U.S. Pat. No.6,307,815) or bonded to a semiconductor or glass-like substrate having achamber to house, accommodate or cover the mechanical structure (see,for example, U.S. Pat. Nos. 6,146,917; 6,352,935; 6,477,901; and6,507,082). In this regard, in the context of the hermetically sealedmetal container, the substrate on, or in which, the mechanical structureresides may be disposed in and affixed to the metal container. Incontrast, in the context of the semiconductor or glass-like substratepackaging technique, the substrate of the mechanical structure may bebonded to another substrate whereby the bonded substrates form a chamberwithin which the mechanical structure resides. In this way, theoperating environment of the mechanical structure may be controlled andthe structure itself protected from, for example, inadvertent contact.

[0004] When employing such conventional packaging techniques, theresulting MEMS tend to be quite large due primarily to packagingrequirements or constraints. In this regard, conventional MEMS packagingtechniques often produce finished devices that are quite large relativeto the small mechanical structure. In the context of packaging in ametal container, this is due to the size of the container itself sinceit is quite large relative to the mechanical structure. Where the MEMSemploys a substrate packaging technique, the substrate on or in whichthe mechanical structure resides must have a sufficient periphery topermit or facilitate the two substrates to be bonded using, for example,epoxy, fusion, glass frit or anodic techniques. That periphery tends tosignificantly increase the size of the resulting MEMS.

[0005] The operation of the MEMS depends, to some extent, on theenvironment in which the mechanical structure is contained and is tooperate (for example, the pressure within the metal container). MEMSsuch as accelerometers tend to operate more effectively in high dampingenvironments whereas gyroscopes and resonators tend to operate moreeffectively in low damping environments. Accordingly, the mechanicalstructures that comprise the accelerometer are often packaged in a highpressure environment. In contrast, the mechanical structures thatcomprise gyroscopes and resonators are often packaged and maintained ina low pressure environment. For example, when gyroscopes and resonatorsare packaged in a metal container, the pressure in the container isreduced, and often the ambient gases are substantially evacuated, priorto sealing.

[0006] There is a need for MEMS (for example, gyroscopes, resonators,temperature sensors and/or accelerometers) that (1) overcome one, someor all of the shortcomings of the conventional packaging techniques and(2) include a controlled or controllable environment for proper,enhanced and/or optimum operation of the mechanical structures.

SUMMARY OF THE INVENTION

[0007] There are many inventions described and illustrated herein. In afirst principal aspect, the present invention is a method of sealing achamber of an electromechanical device (for example, amicroelectromechanical or a nanoelectromechanical device) having amechanical structure, wherein the mechanical structure is in the chamberand the chamber includes a fluid that is capable of providing mechanicaldamping for the mechanical structure. The method of this aspect of theinvention includes depositing a first encapsulation layer over asacrificial layer that is disposed over at least a portion of themechanical structure. At least one vent is formed through theencapsulation layer to expose at least a portion of the sacrificiallayer and at least a portion of the sacrificial layer is removed to formthe chamber. The method further includes introducing at least onerelatively stable gas into the chamber while depositing a secondencapsulation layer over or in the vent whereby when the chamber issealed, the fluid within the chamber includes the relatively stablegas(es).

[0008] In one embodiment, the relatively stable gas(es) may be helium,nitrogen, neon, argon, krypton, xenon and/or perfluorinatedhydrofluorocarbons (for example, CF₄ and C₂F₆), and/or combinationsthereof. In a preferred embodiment, the relatively stable gas(es)includes a low diffusivity.

[0009] In another embodiment of this aspect of the invention, the secondencapsulation layer may include a silicon-bearing compound, for example,monocrystalline silicon, polycrystalline silicon, silicon dioxide,silicon carbide, silicides, BPSG, PSG or silicon nitride. The secondencapsulation layer may be deposited using an epitaxial or a CVDreactor.

[0010] In another principal aspect, the present invention is a method ofsealing a chamber of an electromechanical device (for example, amicroelectromechanical or a nanoelectromechanical device) having amechanical structure, wherein the mechanical structure is in the chamberand wherein the chamber includes a fluid that is capable of providingmechanical damping for the mechanical structure. The method of thisaspect of the invention includes depositing a first encapsulation layerover the mechanical structure, forming at least one vent through theencapsulation layer and forming the chamber. The method further includesdepositing a second encapsulation layer by introducing at least onegaseous deposition reagent into an epitaxial or CVD reactor to therebyform a second encapsulation layer over or in the vent to thereby sealthe chamber. The fluid within the chamber includes at least oneby-product resulting from depositing a second encapsulation layer andwherein the pressure of the fluid is sufficient to provide apredetermined mechanical damping for the mechanical structure.

[0011] In one embodiment, the method further includes introducing atleast one relatively stable gas into the chamber while depositing thesecond encapsulation layer over or in the vent. The fluid in the chambermay also include the relatively stable gas(es), in addition to theby-product resulting from depositing a second encapsulation layer. Inone embodiment, the relatively stable gas(es) may be helium, nitrogen,neon, argon, krypton, xenon and/or perfluorinated hydrofluorocarbons.

[0012] The second encapsulation layer of this aspect of the presentinvention may include a silicon-bearing compound, for example, apolycrystalline silicon, silicon dioxide, silicon carbide, silicides,BPSG, PSG or silicon nitride. The second encapsulation layer may bedeposited using an epitaxial or a CVD reactor. Indeed, the method mayalso include heating the fluid in the chamber to adjust the pressure ofthe fluid to be within a predetermined range of pressures.

[0013] In yet another principal aspect, the present invention is anelectromechanical device, for example, a microelectromechanical ornanoelectromechanical device, including a chamber having a firstencapsulation layer disposed thereon. The first encapsulation layerincludes at least one vent. The electromechanical device also includes amechanical structure, which is disposed in the chamber. A secondencapsulation layer, deposited over or in the vent, seals the chamberwherein the chamber includes at least one relatively stable gas (forexample, helium, nitrogen, neon, argon, krypton, xenon or perfluorinatedhydrofluorocarbons (such as, CF₄ and C₂F₆), and/or combinationsthereof).

[0014] In one embodiment, the second encapsulation layer is depositedusing an epitaxial, a sputtering or a CVD reactor. In anotherembodiment, the first encapsulation layer is also deposited using anepitaxial, a sputtering or a CVD reactor.

[0015] In yet another embodiment, the second encapsulation layer is asilicon-bearing compound, for example, monocrystalline silicon,polycrystalline silicon, silicon dioxide, BPSG, PSG, silicon nitride,silicon carbide or silicides.

[0016] The electromechanical device of this aspect of the presentinvention may include a third encapsulation layer, disposed over thesecond encapsulation layer, to reduce the diffusion of the fluid. In oneembodiment, the third encapsulation layer is a metal (for example,aluminum, chromium, gold, silver, molybdenum, platinum, palladium,tungsten, titanium, and/or copper), metal oxide (for example, aluminumoxide, tantalum oxide, and/or indium oxide), metal alloy (for example,titanium-nitride, titanium-tungsten and/or Al—Si—Cu) and/ormetal-silicon compound (for example, silicides such as tungstensilicide, titanium silicide, and/or nickel silicide) (hereinafter,collectively called “metal bearing material(s)”) which is depositedusing an epitaxial, a sputtering or a CVD reactor. In anotherembodiment, the third encapsulation layer is at least one ofmonocrystalline silicon, polycrystalline silicon, silicon dioxide, BPSG,PSG, silicon nitride or silicon carbide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the course of the detailed description to follow, referencewill be made to the attached drawings. These drawings show differentaspects of the present invention and, where appropriate, referencenumerals illustrating like structures, components, materials and/orelements in different figures are labeled similarly. It is understoodthat various combinations of the structures, components, materialsand/or elements, other than those specifically shown, are contemplatedand are within the scope of the present invention.

[0018]FIG. 1 is a block diagram of microelectromechanical systemdisposed on a substrate, in conjunction with interface circuitry anddata processing electronics;

[0019]FIG. 2 illustrates a top view of a portion of micromechanicalstructure, for example, or portion of the interdigitated or comb-likefinger electrode arrays of an accelerometer;

[0020]FIG. 3 illustrates a cross-sectional view of the portion of theinterdigitated or comb-like finger electrode array of FIG. 2, sectionedalong dotted line a-a, in accordance with certain aspect of the presentinvention;

[0021]FIGS. 4A-4F illustrate cross-sectional views of the fabrication ofthe microstructure of FIG. 3 at various stages of an encapsulationprocess, according to certain aspects of the present invention;

[0022]FIG. 5 illustrates a cross-sectional view of the portion of theinterdigitated or comb-like finger electrode array of FIG. 2, sectionedalong dotted line a-a, in accordance with another aspect of the presentinvention where the first and second encapsulation layers are comprisedof the same material;

[0023]FIG. 6 illustrates a cross-sectional view of the portion of theinterdigitated or comb-like finger electrode array of FIG. 2, sectionedalong dotted line a-a, in accordance with another aspect of the presentinvention where encapsulation layers are annealed such that theencapsulation layers have the properties of a layer that was depositedin one or substantially one processing step;

[0024]FIGS. 7A, 7B, and 8A-8C illustrate cross-sectional views of aportion of the fabrication of the interdigitated or comb-like fingerelectrode array microstructure of FIG. 2, sectioned along dotted linea-a, in accordance with another aspect of the present invention whereencapsulation layers include three or more layers;

[0025]FIG. 9 illustrates a cross-sectional view of a portion of aplurality of micromechanical structures, each having one or moreelectromechanical systems, which are monolithically integrated on orwithin the substrate of a MEMS, in accordance with certain aspect of thepresent invention.

DETAILED DESCRIPTION

[0026] There are many inventions described and illustrated herein. Inone aspect, the present invention is directed to a technique offabricating or manufacturing MEMS having mechanical structures thatoperate in controlled or predetermined mechanical damping environments.In this regard, the present invention encapsulates the mechanicalstructures within a chamber, prior to final packaging and/or completionof the MEMS. The environment within the chamber containing and/orhousing the mechanical structures provides the predetermined, desiredand/or selected mechanical damping. The parameters (for example,pressure) of the encapsulated fluid (for example, a gas or a gas vapor)in which the mechanical structures are to operate are controlled,selected and/or designed to provide a desired and/or predeterminedoperating environment.

[0027] In one embodiment, one or more relatively stable gases, having aselected, desired and/or predetermined state(s), are introduced duringthe encapsulation process. The relatively stable gas(es) experienceslittle to no reaction, during the encapsulation process, with, forexample, the mechanical structures, materials used to encapsulate themechanical structures (i.e., the deposition reagents) and/or theproducts produced during the process (whether in a gas or solid form).As such, once the chamber containing and/or housing the mechanicalstructures is “sealed” by way of the encapsulation process, therelatively stable gas is “trapped” within the chamber. The state of thegas(es) within the chamber determine, to a significant extent, thepredetermined, desired and/or selected mechanical damping of themechanical structures.

[0028] This relatively stable gas(es), for example, helium, nitrogen,neon, argon, krypton, xenon and/or perfluorinated hydrofluorocarbons(for example, CF₄ and C₂F₆), may comprise the majority, all orsubstantially all of the fluid within the sealed chamber (i.e., thechamber containing the encapsulated mechanical structures). In apreferred embodiment, the relatively stable gas(es) includes a low,well-known and/or controllable diffusivity during and afterencapsulation process. In this way, the state of the gas(es) may becontrolled, selected and/or designed to provide a desired and/orpredetermined environment over the operating lifetime of the finishedMEMS and/or after, for example, subsequent micromachining processing(for example, high temperature processes).

[0029] In another embodiment, one or more gases are introduced duringthe encapsulation process with the expectation that those gases willreact with the environment during and/or after the encapsulationprocess. In this embodiment, the predetermined gases react and/orcombine with gas(es), material(s) and/or by-product(s) resulting from,or produced during the encapsulation process, to provide a desiredand/or predetermined fluid (having a desired, selected and/orpredetermined state) that is trapped within the “sealed” chambercontaining the encapsulated mechanical structures. In this way, thefluid, having a selected, desired and/or predetermined state, resides oris maintained within the chamber containing the mechanical structuresand provides a desired, predetermined and/or selected mechanical dampingfor those structures.

[0030] The one or more gases may be a primary or a secondary reagent inthe forming, growing and/or depositing the encapsulation layer(s).Alternatively, (or in addition to) these gases may be additional gasesthat are not significant in forming, growing and/or depositing theencapsulation layer(s). In this regard, these additional gases may reactwith materials (solids and/or gases) in the deposition environment toproduce by-product(s) that are trapped in the chamber afterencapsulation.

[0031] It should be noted that the state of the fluid that is trappedmay be adjusted, modified and/or controlled by subsequent processingsteps. In this regard, the state of the fluid (for example, thepressure) immediately after encapsulation may be adjusted, modifiedand/or controlled by a subsequent micromachining and/or integratedcircuit processing which may cause or promote, for example, (1)additional reaction(s) between the “trapped” fluid and the otherelements of the environment within the chamber (for example, thematerial surrounding or comprising the mechanical structures) and/or (2)diffusion of the “trapped” fluid or by-products thereof. As such, incertain embodiments, the fluid that is trapped within the sealed chambermay undergo further change during and/or after encapsulation processsuch that, after completion of the MEMS, the state of the fluid withinthe sealed chamber provides the desired, predetermined and/or selectedmechanical damping for the mechanical structures. Thus, in theseembodiments, the state of the fluid may be adjusted, modified and/orcontrolled to provide the desired and/or predetermined environment overthe operating lifetime of the finished MEMS and/or after subsequentmicromachining and/or integrated circuit processing.

[0032] With reference to FIG. 1, in one exemplary embodiment, a MEMS 10includes a micromachined mechanical structure 12 that is disposed onsubstrate 14, for example, an undoped semiconductor-like material, aglass-like material, or an insulator-like material. The MEMS 10 may alsoinclude data processing electronics 16, to process and analyzeinformation generated by micromachined mechanical structure 12. Inaddition, MEMS 10 may also include interface circuitry 18 to provide theinformation from micromachined mechanical structure 12 and/or dataprocessing electronics 16 to an external device (not illustrated), forexample, a computer, indicator or sensor.

[0033] The data processing electronics 16 and/or interface circuitry 18may be integrated in or on substrate 14. In this regard, MEMS 10 may bea monolithic structure including mechanical structure 12, dataprocessing electronics 16 and interface circuitry 18. The dataprocessing electronics 16 and/or interface circuitry 18 may also resideon a separate, discrete substrate that, after fabrication, is bonded toor on substrate 14.

[0034] With reference to FIG. 2, in one embodiment, micromachinedmechanical structure 12 includes mechanical structures 20 a-d disposedon, above or in substrate 14. The micromachined mechanical structure 12may be an accelerometer, gyroscope or other transducer (for example,pressure sensor, tactile sensor or temperature sensor). Themicromachined mechanical structure 12 may also include mechanicalstructures of a plurality of transducers or sensors including one ormore accelerometers, gyroscopes, pressure sensors, tactile sensors andtemperature sensors. Where micromachined mechanical structure 12 is anaccelerometer, mechanical structures 20 a-d may be a portion of theinterdigitated or comb-like finger electrode arrays that comprise thesensing features of the accelerometer (See, for example, U.S. Pat. No.6,122,964).

[0035]FIG. 3 illustrates a cross-sectional view of micromachinedmechanical structure 12, including mechanical structures 20 a-d, alongdotted line a-a′. With reference to FIG. 3, in one embodiment,mechanical structures 20 a-d are disposed within chamber 22 containingfluid 24, having a selected, desired and/or predetermined state, that is“trapped”, “sealed”, and/or contained within chamber 22. The fluid 24provides an environment for mechanical structures 20 a-d with a desired,predetermined, appropriate and/or selected mechanical damping.

[0036] It should be noted that the mechanical structures of one or moretransducers or sensors (for example, accelerometers, gyroscopes,pressure sensors, tactile sensors and/or temperature sensors) may becontained or reside in a single chamber. Under this circumstance, fluid24 in chamber 22 provides a desired, predetermined, appropriate and/orselected mechanical damping for the mechanical structures of one or moremicromachined mechanical structures (for example, an accelerometer, apressure sensor, a tactile sensor and/or temperature sensor).

[0037] Moreover, the mechanical structures of the one or moretransducers or sensors may themselves include multiple layers that arevertically stacked and/or interconnected. (See, for example,micromachined mechanical structure 12 b of FIG. 9). Thus, under thiscircumstance, the mechanical structures are fabricated using one or moreprocessing steps to provide the vertically stacked and/or interconnectedmultiple layers.

[0038] In one embodiment, fluid 24 is primarily one or more relativelystable gases (for example, helium, nitrogen, neon, argon, krypton, xenonand/or perfluorinated hydrofluorocarbons such as, CF₄ and C₂F₆). Inanother embodiment, fluid 24 is one or more gases or gas/fluidproduct(s) (for example, SiH₄+O₂→SiO₂+H₂O+O₂) that are used in, resultfrom or are produced by or during, the encapsulation process and/or asubsequent fabrication process or processes. Indeed, fluid 24 may be acombination of one or more relatively stable gases and one or more othergases or product(s) that result from, or are produced by, theencapsulation process.

[0039] The encapsulating layers 26 a and 26 b may be comprised of, forexample, a semiconductor, an insulator or a metal bearing material. Forexample, the encapsulating layers 26 a and 26 b may contain silicon (forexample, monocrystalline silicon, polycrystalline silicon or amorphoussilicon, whether doped or undoped), and/or nitrogen (for example, asilicon nitride) and/or oxygen (for example, a silicon dioxide). Othermaterials are suitable for encapsulating or sealing chamber 22 (forexample, germanium, silicon/germanium, silicon carbide (SiC), andgallium arsenide). Indeed, all materials that are capable ofencapsulating chamber 22 and providing an adequate barrier to diffusionof fluid 24, whether now known or later developed, are intended to bewithin the scope of the present invention.

[0040] The encapsulating layers 26 a and 26 b may be the same materialsor different materials. The encapsulating layers 26 a and 26 b may bedeposited, formed or grown using the same or different techniques. Forexample, encapsulating layer 26 a may be a polycrystalline silicondeposited using a low pressure (“LP”) chemically vapor deposited (“CVD”)process or plasma enhanced (“PE”) CVD process and encapsulating layer 26b may be a polycrystalline silicon deposited using an atmosphericpressure (“AP”) CVD process. Alternatively, for example, encapsulatinglayer 26 a may be a silicon dioxide deposited using a LPCVD process andencapsulating layer 26 b may be a doped silicon dioxide (for example,phosphosilicate (“PSG”) or borophosphosilicate (“BPSG”)) using a PECVDprocess. Indeed, encapsulating layer 26 a may be a polycrystallinesilicon or doped silicon dioxide (for example, PSG or BPSG) using aPECVD process and encapsulating layer 26 b may be a silicon dioxidedeposited using a LPCVD. Thus, all materials and deposition techniques,and permutations thereof, for encapsulating chamber 22, whether nowknown or later developed, are intended to be within the scope of thepresent invention.

[0041] It should be noted that the encapsulating layers 26 a and/or 26 bmay be selected in conjunction with the selection of the one or morepredetermined gases in order to provide the gas/fluid product(s) thatresult from or are produced by the encapsulation process and/orsubsequent fabrication process(es). For example, employing SiH₄+O₂ mayproduce encapsulating layer 26 b of SiO₂ and fluid 24 of H₂O+O₂. Inanother embodiment, employing SiO₄(CH₄)_(x)+O₂ may produce encapsulatinglayer 26 b of SiO₂ and fluid 24 of O₂+various carbon containingby-products.

[0042] With reference to FIG. 4A, the exemplary method of fabricating ormanufacturing a micromachined mechanical structure 12 may begin with apartially formed device including mechanical structures 20 a-d disposedon sacrificial layer 28, for example, silicon dioxide. Mechanicalstructures 20 a-d and sacrificial layer 28 may be formed using wellknown deposition, lithographic, etching and/or doping techniques.

[0043] With reference to FIGS. 4B, 4C and 4D, following formation ofmechanical structures 20 a-d, second sacrificial layer 30, for example,silicon dioxide or silicon nitride, may be deposited to secure, spaceand/or protect mechanical structures 20 a-d during subsequentprocessing. Thereafter, first encapsulation layer 26 a may be depositedon second sacrificial layer 30 (see, FIG. 4C) and etched (see, FIG. 4D)to form passages or vents 32 to permit etching and/or removal ofselected portions of first and second sacrificial layers 28 and 30,respectively.

[0044] With reference to FIGS. 4D and 4E, first and second sacrificiallayers 28 and 30, respectively, may be etched to remove selectedportions of layers 28 and 30 and release mechanical structures 20 a-d.For example, in one embodiment, where first and second sacrificiallayers 28 and 30 are comprised of silicon dioxide, selected portions oflayers 28 and 30 may be removed/etched using well known wet etchingtechniques and buffered HF mixtures (i.e., a buffered oxide etch) orwell known vapor etching techniques using vapor HF. Proper design ofmechanical structures 20 a-d and sacrificial layers 28 and 30, andcontrol of the HF etching process parameters may permit the sacrificiallayer 28 to be sufficiently etched to remove all or substantially all oflayer 28 around mechanical elements 20 a-d and thereby releasemechanical elements 20 a-d to permit proper operation of MEMS 10.

[0045] In another embodiment, where first and second sacrificial layers28 and 30 are comprised of silicon nitride, selected portions of layers28 and 30 may be removed/etched using phosphoric acid. Again, properdesign of mechanical structures 20 a-d and sacrificial layers 28 and 30,and control of the wet etching process parameters may permit thesacrificial layer 28 to be sufficiently etched to remove all orsubstantially all of sacrificial layer 28 around mechanical elements 20a-d which will release mechanical elements 20 a-d.

[0046] It should be noted that there are: (1) many suitable materialsfor layers 28 and/or 30 (for example, silicon dioxide, silicon nitride,and doped and undoped glass-like materials, e.g., PSG, BPSG, and spin onglass (“SOG”)), (2) many suitable/associated etchants (for example, abuffered oxide etch, phosphoric acid, and alkali hydroxides such as, forexample, NaOH and KOH), and (3) many suitable etching or removaltechniques (for example, wet, plasma, vapor or dry etching), toeliminate, remove and/or etch sacrificial layers 28 and/or 30. Indeed,layers 28 and/or 30 may be a doped or undoped semiconductor (forexample, polysilicon, germanium or silicon/germanium) in those instanceswhere mechanical structures 20 a-d are the same or similarsemiconductors (i.e., processed, etched or removed similarly) providedthat mechanical structures 20 a-d are not affected by the etching orremoval processes (for example, where structures 20 a-d are “protected”during the etch or removal process (e.g., an oxide layer protecting asilicon based structures 20 a-d) or where structures 20 a-d arecomprised of a material that is neither affected nor significantlyaffected by the etching or removal process of layers 28 and/or 30).Accordingly, all materials, etchants and etch techniques, andpermutations thereof, for eliminating, removing and/or etching, whethernow known or later developed, are intended to be within the scope of thepresent invention.

[0047] With reference to FIG. 4F, after releasing mechanical elements 20a-d, second encapsulation layer 26 b may be deposited, formed and/orgrown. The second encapsulation layer 26 b may be, for example, asilicon-based material (for example, a polysilicon or silicon dioxide),which is deposited using, for example, an epitaxial, a sputtering or aCVD-based reactor (for example, APCVD, LPCVD, or PECVD). The deposition,formation and/or growth may be by a conformal process or non-conformalprocess. The material may be the same as or different from firstencapsulation layer 26 a. However, it may be advantageous to employ thesame material to form first and second encapsulation layers 26 a and 26b (see, FIG. 5). In this way, the thermal expansion rates are the sameand the boundaries between layers 26 a and 26 b may enhance the “seal”of chamber 24.

[0048] In one set of embodiments, during the deposition of secondencapsulation layer 26 b, in addition to the gases that are employed toform, deposit and/or grow layer 26 b (for example, SiH₄→Si+2H₂), one ormore relatively stable gases (for example, helium, nitrogen, neon,argon, xenon, and/or perfluorinated hydrofluorocarbons) are introducedat a predetermined pressure and flow rate. These relatively stable gasesare trapped or encapsulated in chamber 22, during the encapsulationprocess, to form part or all of fluid 24. As mentioned above, fluid 24provides an environment for mechanical structures 20 a-d with a desired,predetermined and/or selected mechanical damping.

[0049] In certain embodiments, the one or more relatively stable gaseshave or cause little to no reaction during the encapsulation process.For example, the relatively stable gas does not significantly react withmechanical structures 20 a-d (for example, the sidewalls of structures20 a-d), the gases/materials used to encapsulate/seal the mechanicalstructures 20 a-d (for example, silicon, oxygen or nitrogen), firstencapsulation layer 26 a, and/or second encapsulation layer 26 b whichis formed, deposited and/or grown during the encapsulating/sealingprocess. Thus, in these embodiments, once chamber 22 containing and/orhousing the mechanical structures 20 a-d is “sealed” (i.e., afterdeposition of second encapsulation layer 26 b), the relatively stablegas is “trapped” within chamber 22 and provides (or will provide after,for example, subsequent processing steps that finalize the environment)mechanical structures 20 a-d with a selected, designed and/orpredetermined mechanical damping parameter.

[0050] The relatively stable gas(es) may be, for example, any gas (orgas compound) that is relatively stable or controllable: (1) duringformation, deposition and/or growth of second encapsulation layer 26 b(for example, at the pressure and temperature of the process and withthe reagents of that process) and/or (2) with respect to the environmentwithin chamber 22 (for example, causes little to no reaction with firstencapsulation layer 26 a (for example, silicon dioxide or othersilicon-based material). In this way, the one or more relatively stablegases will not react, or will only minimally react, with the depositionreagents, the products, the encapsulated mechanical structure 12 and/orthe encapsulation walls during (and, preferably after) formation,deposition and/or growth of second encapsulation layer 26 b.

[0051] In a preferred embodiment, the one or more relatively stablegases may be helium, nitrogen, neon, argon, krypton, xenon and/orperfluorinated hydrofluorocarbons (for example, CF₄ and C₂F₆). Therelatively stable gas(es) may comprise some, a majority, all orsubstantially all of fluid 24 within chamber 22 after sealing orisolating chamber 22.

[0052] As discussed in detail below, the state of the gas(es) during theencapsulation process may determine the parameters of the gas(es) (andthe mechanical damping parameter of the MEMS 10) when sealed withinchamber 22. In this regard, the temperature of the encapsulation processand the partial pressure of the relatively stable gas(es) may have asignificant impact on the pressure of fluid 24 after encapsulation. Assuch, in those situations where a relatively high mechanical damping isdesired (for example, where micromachined mechanical structure 12 is anaccelerometer that requires a low quality factor (Q), it may beadvantageous to employ fabrication techniques for forming, depositingand/or growing second encapsulation layer 26 b having low temperaturesand high pressures. In this way, the final pressure of fluid 24 inchamber 22 may be relatively high.

[0053] For example, in one embodiment, where second encapsulation layer26 b is a silicon dioxide (or other insulator, for example, siliconnitride) using LPCVD techniques facilitates “sealing” chamber 22 at arelatively low temperature. In this regard, LPCVD may generally beoperated between 100 to 500 Pa and at a relatively low temperature,typically 500° C. to 600° C. In another embodiment, an APCVD may beemployed to deposit doped and undoped oxides (for example, BPSG, PSG,and/or SiO₂) at relatively high pressures (100 to 10 k Pa) and lowtemperatures (350° C. to 400° C.). In those instances where secondencapsulation layer 26 b is a silicon-based material (polysilicon,silicon carbide, silicon dioxide, and/or silicon nitride), an epitaxyreactor may be employed to deposit such a material at pressures between1 to 2 atmospheres and temperatures between 400° C. to 1200° C.

[0054] It should be noted that there are many deposition techniques andmaterials that are suitable for forming, depositing and/or growingsecond encapsulation layer 26 b. For example, a PECVD technique may beemployed to deposit, for example, doped and undoped oxides, siliconnitride silicon carbide, and/or polysilicon at suitable pressures andtemperatures. All materials and formation, deposition and growthtechniques, and permutations thereof, for forming, depositing and/orgrowing second encapsulation layer 26 b, whether now known or laterdeveloped, are intended to be within the scope of the present invention.

[0055] In those situations where micromachined mechanical structure 12undergoes or experiences additional micromachining processing, it may beadvantageous to employ one or more relatively stable gases that includea low, well-known and/or controllable diffusivity. For example, gaseshaving larger or heavier molecules (for example, nitrogen, neon, argon,krypton, xenon or perfluorinated hydrofluorocarbons (for example, CF₄and C₂F₆)) may be less susceptible to diffusion, via first encapsulationlayer 26 a and/or second encapsulation layer 26 b (and/or at theboundaries thereof), during and after the encapsulation process. In thisway, the state of fluid 24 may be controlled, selected and/or designedto provide the desired and/or predetermined environment after, forexample, subsequent micromachining processing (for example, hightemperature processes) and/or over the operating lifetime of thefinished MEMS 10. This may provide MEMS 10 that has or exhibits a morestable and precise operation.

[0056] It should be noted that where micromachined mechanical structure12 undergoes or is subjected to micromachining processing that mayimpact the environment within chamber 22, fluid 24 may diffuse throughencapsulation layer 26 a and/or encapsulation layer 26 b. That diffusionmay cause or result in a “final” ambient pressure of fluid 24 (i.e., thepressure of fluid 24 after completion of MEMS 10) being below or outsideof the selected, predetermined and/or desired range of pressures. Assuch, in one embodiment, the ambient pressure of fluid 24 immediatelyafter being “trapped” or “sealed” in chamber 24 may be selected ordesigned to be greater than the selected, predetermined and/or desiredrange of mechanical damping of micromachined mechanical structure 12required or desired during normal operation. Thus, after any diffusionof fluid 24, as a result of additional processing, the “final” ambientpressure of fluid 24 may be within the selected, predetermined and/ordesired range of pressures. In this way, the subsequent micromachiningprocessing causes a reduction in pressure of fluid 24 such that the“final” pressure of fluid 24 provides the selected, designed orpredetermined mechanical damping of micromachined mechanical structure12.

[0057] It should be further noted that in those situations where secondencapsulation layer 26 b (and first encapsulation layer 26 a) arecomprised of a dense material, it may be advantageous to employrelatively stable gas(es) such as hydrogen and/or helium in addition to,or in lieu of, for example, nitrogen, neon, argon, krypton, xenon and/orperfluorinated hydrofluorocarbons (for example, CF₄ and C₂F₆). A secondencapsulation layer 26 b (and first encapsulation layer 26 a) that iscomprised of a dense material, for example, silicon carbide, siliconnitride, or metal bearing material, may provide a sufficient barrier todiffusion which thereby permits use of relatively stable gases that arelight, have small molecules and are relatively inexpensive andavailable, such as hydrogen and/or helium.

[0058] In another set of embodiments, during the deposition, growthand/or formation of second encapsulation layer 26 b, one or moregases/materials are introduced to form, deposit and/or grow secondencapsulation layer 26 b (for example, SiH₄→Si+2H₂), with theexpectation that these gases will react during the encapsulation processto provide a resulting fluid (having a desired, selected and/orpredetermined state) that is trapped within chamber 22—after secondencapsulation layer 26 b “seals” chamber 22. In these embodiments, thepredetermined gas/material are primary or secondary reagents of thedeposition process and, in addition to being major/secondaryconstituents in the formation of second encapsulation layer 26 b, alsoprovide fluid 24 (having a desired, selected and/or predetermined state)that is “trapped” within chamber 22. In this way, fluid 24 provides adesired, predetermined and/or selected mechanical damping for thestructures 20 a-d.

[0059] Thus, in these embodiments, the predetermined gas/material areprimary or secondary reagents of the deposition process to react and/orcombine with a gas, material(s) and/or by-product(s) produced during theencapsulation process.

[0060] For example, in one embodiment, where the second encapsulationlayer 26 b is silicon dioxide (for example, SiH₄+O₂→SiO₂+H₂O+O₂), anAPCVD may be employed to deposit the oxide at relatively high pressures(100 to 10 kPa) and low temperatures (350° C. to 400° C.). The residualH₂O+O₂ (i.e., fluid 24) may be “trapped” in chamber 22 at a relativelyhigh pressure and relatively low temperature. Indeed, where necessary ordesired, the pressure of fluid 24 may be adjusted or modified duringsubsequent processing steps to provide the desired, predetermined and/orselected mechanical damping for mechanical structures 20 a-d.

[0061] In another embodiment, an epitaxy reactor may be employed todeposit the second encapsulation layer 26 b as a polysilicon atpressures between 1 to 2 atmospheres and temperatures between 400° C. to1200° C. (for example, SiCl₄ (gas)+2H₂→Si (solid)+4HCl (gas)). The fluid24 (i.e., 4HCl) may be “trapped” in chamber 22 at a desired,predetermined and/or selected pressure and relatively low temperature.As such, fluid 24, having a selected, desired and/or predeterminedstate, may provide a desired, predetermined and/or selected mechanicaldamping for the structures 20 a-d.

[0062] As mentioned above, there are many deposition techniques andmaterials that are suitable for forming, depositing and/or growingsecond encapsulation layer 26 b. For example, a CVD technique may beemployed to deposit, for example, doped and undoped oxides (for example,SiO₄(CH₄)_(x)+O₂→SiO₂ (encapsulating layer 26 b)+O₂ (fluid 24)+a carbonby-product (fluid 24)), as well as silicon nitride and/or polysilicon.Accordingly, all materials and formation, deposition and growthtechniques, and permutations thereof, for forming, depositing and/orgrowing second encapsulation layer 26 b, whether now known or laterdeveloped, are intended to be within the scope of the present invention.

[0063] It should be noted that the residual gas(es) may be trapped inchamber 22 at a desired, predetermined and/or selected pressure.Moreover, where the trapped gas(es) is not at a (or within a range of)desired, predetermined and/or selected “final” pressure, the pressure ofthe gas(es) may be modified, changed and/or controlled, via subsequentprocess (for example, high temperature processing that causes diffusionor further/continuing reactions), so that the “completed” MEMS 10includes a micromachined mechanical structure 12 that is properly damped(i.e., at, or within a range of, the desired, predetermined and/orselected mechanical damping for structure 12). Thus, the state of fluid24 (for example, the pressure of fluid 24) immediately afterencapsulation may be adjusted, modified and/or controlled by asubsequent micromachining and/or integrated circuit processing. In thisway, the state of fluid 24 may be adjusted, modified and/or controlledto provide a desired and/or predetermined environment over the operatinglifetime of the finished MEMS and/or after subsequent micromachiningand/or integrated circuit processing.

[0064] In another set of embodiments, the one or more additionalgases/materials react with the environment (for example, solids and/orgases in and/or around micromachined mechanical structure 12, mechanicalstructures 20 a-d and/or chamber 22) to provide fluid 24 that is“trapped” in chamber 22 after chamber 22 is “sealed”. However, in theseembodiments, the one or more gases/materials do not have a significantrole in forming, growing and/or depositing encapsulation layer 26 b. Inthese embodiments, the predetermined gas/material are in addition to theprimary or secondary reagents of the deposition process and react withthe environment during encapsulation to provide fluid 24 (having adesired, selected and/or predetermined state) that is “trapped” withinchamber 22. As mentioned above, fluid 24 provides a desired,predetermined and/or selected mechanical damping for structures 20 a-d.

[0065] For example, in one embodiment, where second encapsulation layer26 b is silicon dioxide (for example, O₂+2Si→SiO₂+2SiO) an APCVD may beemployed to deposit the oxide at relatively high pressures (100 to 10kPa) and low temperatures (350° C. to 400° C.). The residual 2SiO (i.e.,fluid 24) may be “trapped” in chamber 22 at a relatively high pressureand relatively low temperature. As mentioned above, where necessary ordesired, the pressure of fluid 24 may also be adjusted or modifiedduring subsequent processing steps to provide the desired, predeterminedand/or selected mechanical damping for mechanical structures 20 a-d. Asmentioned above, in those situations where a relatively high mechanicaldamping is desired (for example, where micromachined mechanicalstructure 12 is an accelerometer that requires a low Q), it may beadvantageous for the final pressure of fluid 24 in chamber 22 to berelatively high. As such, where a relatively high pressure of fluid 24is desired, it may be advantageous to employ low temperature techniquesfor depositing, forming and/or growing second encapsulation layer 26 b.In this regard, as the sealing temperature is decreased, the pressure atthe operating temperature will increase by approximately the ratio ofthe absolute temperatures. As such, lower “sealing” temperatures maycontribute to a higher pressure of fluid 24 when chamber 22 is “sealed”.

[0066] Moreover, it may be important that the partial pressure of thegas/material that comprises fluid 24 be relatively high so that thepressure of fluid 24 that resides or is “trapped” in “sealed” chamber 22is relatively high. In this regard, as the partial pressure of the gas(for example, the relatively stable gas) increases during theencapsulation or chamber sealing process (i.e., during the deposition,formation and/or growth of second encapsulation layer 26 b), thepressure of fluid 24 in chamber 22 increases proportionally. As such, itmay be advantageous to minimize or reduce the flow of other processgases during the encapsulation process in those situations where it isdesired to have a high final pressure of fluid 24.

[0067] It should also be noted that, in those situations where a highfinal pressure of fluid 24 is desired, it may also be advantageous toimplement the encapsulation process (i.e., the process of depositing,forming and/or growing second encapsulation layer 26 b) at a high,elevated and/or maximum total pressure to enhance and/or maximize thefinal pressure of fluid 24. In this way, a relatively high mechanicaldamping of micromachined mechanical structure 12 may be achieved.

[0068] It should be further noted that, in certain embodiments, theencapsulation layer that “traps” and “seals” fluid 24 in chamber 22 maybe sufficiently annealed to function as if the encapsulation layers 26 aand 26 b were deposited, formed and/or grown during one or substantiallyone processing step (see, FIG. 6). Such an encapsulation layer mayprovide a better “seal” of chamber 22 so that fluid 24 is lesssusceptible to diffusion over the lifetime of the MEMS and/or underharsh external operating environments. Moreover, the encapsulationprocess of chamber 22 may include three or more encapsulation layers.With reference to FIGS. 7A and 7B, in another set of embodiments, asecond encapsulation layer 26 b may be deposited, formed and/or grown.In this set of embodiments, however, second encapsulation layer 26 bdoes not entirely “seal” chamber 22. Rather, a third encapsulation layer26 c (or subsequent layer 26 x) “seals” chamber 22 and “traps” fluid 24in chamber 22.

[0069] The second encapsulation layer 26 b may be, for example, asemiconductor material (for example, a monocrystalline, polycrystallinesilicon or germanium), an insulator material (for example, silicondioxide, silicon nitride, BPSG, or PSG) or metal bearing material (forexample, suicides or TiW), which is deposited using, for example, anepitaxial, a sputtering or a CVD-based reactor (for example, APCVD,LPCVD or PECVD). The deposition, formation and/or growth may be by aconformal process or non-conformal process. The material comprisingencapsulation layer 26 b may be the same as or different from firstencapsulation layer 26 a.

[0070] Thereafter, third encapsulation layer 26 c may be deposited,formed and/or grown (see, FIG. 7B). The third encapsulation layer 26 cmay “seal” or close chamber 22 and, as such, “trap” fluid 24 (having aselected, desired and/or predetermined state) in chamber 22.

[0071] The deposition, formation and/or growth of third encapsulationlayer 26 c may be the same as, substantially similar to, or differentfrom that of encapsulation layers 26 a and/or 26 b. In this regard,third encapsulation layer 26 c may be comprised of, for example, asemiconductor material, an insulator material, or metal bearingmaterial. The third encapsulation layer 26 c may be deposited using, forexample, an epitaxial, a sputtering or a CVD-based reactor (for example,APCVD, LPCVD or PECVD). The deposition, formation and/or growth processmay be conformal or non-conformal. The material comprising encapsulationlayer 26 c may be the same as or different from first encapsulationlayer 26 a and/or second encapsulation layer 26 b.

[0072] As mentioned above, it may be advantageous to employ the samematerial to form first and second encapsulation layers 26 a and 26 band/or second and third encapsulation layers 26 b and 26 c. In this way,the thermal expansion rates are the same and the boundaries betweenlayers 26 a and 26 b may enhance the “seal” of chamber 24.

[0073] It should be noted that the entire discussion above with respectto fluid 24 and/or fluid 24 in conjunction with FIGS. 3-6 is entirely,fully and completely applicable to this set of embodiments. For the sakeof brevity, it will not be repeated.

[0074] With reference to FIGS. 8A and 8B, in another set of embodiments,encapsulation layer 26 c (FIG. 8A) and encapsulation layer 26 d (FIG.8B) may be deposited, formed and/or grown to enhance the “seal” ofchamber 22 and thereby enhance the barrier to diffusion of fluid 24. Theencapsulation layer 26 c (FIG. 8A) and encapsulation layer 26 d (FIG.8B), alone, or in combination with the other encapsulation layers,“traps” fluid 24 (having a selected, desired and/or predetermined state)in chamber 22.

[0075] The encapsulation layer 26 c (FIG. 8A) and encapsulation layer 26d (FIG. 8B) may be, for example, a semiconductor material (for example,a polysilicon, germanium, or silicon/germanium), an insulator material(for example, silicon dioxide, silicon nitride, BPSG, PSG, or SOG) ormetal bearing material (for example, silicides). The encapsulation layer26 c (FIG. 8A) and encapsulation layer 26 d (FIG. 8B) may be, forexample deposited, formed or grown using, for example, an epitaxial, asputtering or a CVD-based reactor (for example, APCVD, LPCVD or PECVD).The deposition, formation and/or growth may be by a conformal process ornon-conformal process. The material comprising encapsulation layer 26 c(FIG. 8A) and encapsulation layer 26 d (FIG. 8B) may be the same as ordifferent from the other encapsulation layers.

[0076] It should be noted that the discussion above with respect tofluid 24 and/or fluid 24 in conjunction with FIGS. 3-6 is entirely,fully and completely applicable to this set of embodiments. For the sakeof brevity, it will not be repeated.

[0077] It should be further noted that encapsulation layer 26 b (FIG.8A) and encapsulation layer 26 c (FIG. 8B), in addition to or in lieu ofproviding a barrier to diffusion of fluid 24, may be employed to reduce,minimize and/or eliminate any step coverage issues that may be presentedwhen enclosing or “sealing” passages or vents 32 (see, for example,FIGS. 4E, 4F, 7A and 7B) and chamber 22. In this regard, encapsulationlayer 26 b (FIG. 8A) and encapsulation layer 26 c (FIG. 8B) may be amaterial that is deposited, formed and/or grown in a manner thatprovides good, enhanced, adequate and/or sufficient step coverage, forexample, BPSG, PSG or SOG which is deposited using, for example, aCVD-based reactor (for example, APCVD, LPCVD or PECVD). In this way,encapsulation layer 26 b (FIG. 8A) and encapsulation layer 26 c (FIG.8B) may provide, or if necessary may be further processed to provide(for example, a re-flow step), a sufficiently and/or substantiallyplanar surface.

[0078] Thereafter, encapsulation layer 26 c (FIG. 8A) and encapsulationlayer 26 d (FIG. 8B) may be deposited, formed and/or grown usingmaterials and/or techniques (even those having or providing poor stepcoverage) in order to provide an adequate and/or sufficient “seal” ofchamber 22. The encapsulation layer 26 c (FIG. 8A) and encapsulationlayer 26 d (FIG. 8B) alone, or in combination with the otherencapsulation layers, “traps” fluid 24 (having a selected, desiredand/or predetermined state) in chamber 22.

[0079] In addition, with reference to FIG. 8C, an additionalencapsulation layer 26 d may be deposited, formed and/or grown tofurther enhance the “seal” of chamber 22. In this embodiment,encapsulation layer 26 c may provide some, little or no barrier todiffusion of fluid 24 whereas encapsulation layer 26 d presents some, amajority or essentially the entire barrier to diffusion of fluid 24.Thus, encapsulation layer 26 d, alone or together with the otherencapsulation layers (i.e., encapsulation layers 26 a-c), “traps” fluid24 in chamber 22.

[0080] Further, as noted above, encapsulation layers 26 b and/orencapsulation layer 26 c may be employed (alone or in combination) toreduce, minimize and/or eliminate any step coverage issues that may bepresented by enclosing passages or vents 32 and “sealing” chamber 22.The encapsulation layer 26 b and/or encapsulation layer 26 c may providea sufficiently and/or substantially planar surface so that encapsulationlayer 26 c and/or encapsulation layer 26 d may be implemented using awide variety of material(s) and deposition, formation and/or growthtechniques in order to “seal” of chamber 22 and “trap” fluid 24 (havinga selected, desired and/or predetermined state) in chamber 22.

[0081] Accordingly, in this set of embodiments, at least one additionalencapsulation layer 26 d is deposited, formed and/or grown over a fullyencapsulated and “sealed” chamber 22 to provide an additional barrier todiffusion of fluid 24. In this way, fluid 24 is “trapped” in chamber 22and has a selected, desired and/or predetermined state to facilitateproper operation of mechanical structure 12.

[0082] With reference to FIGS. 8A-C, in another set of embodiments,some, a majority, all or substantially all of fluid 24 is “trapped”within chamber 22 (and the state of fluid 24 is established within aselected, predetermined and/or desired range of pressures) afterdepositing, forming or growing encapsulation layer 26 b (FIG. 8A) andencapsulation layer 26 c (FIG. 8B) while depositing, forming or growingencapsulation layer 26 c (FIG. 8A) and encapsulation layer 26 d (FIG.8B). In this set of embodiments, fluid 24 may be diffused into chamber22 after enclosed by encapsulation layer 26 b (FIG. 8A) andencapsulation layer 26 c (FIG. 8B). The state of fluid 24 may beestablished at a pressure that is sufficient to cause a gas to penetrateencapsulation layer 26 b (FIG. 8A) and encapsulation layer 26 c (FIG.8B) and diffuse through that layer and into chamber 24.

[0083] For example, a gas or gas vapor, such as helium, may beintroduced while encapsulation layer 26 c (FIG. 8A) and encapsulationlayer 26 d (FIG. 8B) are being deposited, formed and/or grown. That gasor gas vapor (for example, helium) may be under sufficient pressure todiffuse through encapsulation layer 26 b (FIG. 8A) and encapsulationlayer 26 c (FIG. 8B) into chamber 22. Moreover, after deposition,formation and/or growth of encapsulation layer 26 c (FIG. 8A) andencapsulation layer 26 d (FIG. 8B), the gas or gas vapor may be“trapped” in chamber 22. The encapsulation layer 26 c (FIG. 8A) andencapsulation layer 26 d (FIG. 8B), alone, or in combination with theother encapsulation layers, “traps” fluid 24 (having a selected, desiredand/or predetermined state) in chamber 22.

[0084] Thus, in this set of embodiments, fluid 24 diffuses into chamber22 through encapsulation layer 26 a and/or encapsulation layer 26 b.That diffusion may cause or result in a “final” ambient pressure offluid 24 (i.e., the pressure of fluid 24 after completion of MEMS 10and/or after deposition, formation and/or growth of encapsulation layer26 c (FIG. 8A) and encapsulation layer 26 d (FIG. 8B)) being within aselected, predetermined and/or desired range of pressures.

[0085] In another set of embodiments, the ambient pressure of fluid 24immediately after being “trapped” or “sealed” in chamber 24 may beselected or designed to be less than the selected, predetermined and/ordesired range of mechanical damping of micromachined mechanicalstructure 12 required or desired during normal operation. Afterprocessing encapsulation layer 26 c (FIG. 8A) and encapsulation layer 26d (FIG. 8B), the “final” ambient pressure of fluid 24 may be within theselected, predetermined and/or desired range of pressures. In this way,the subsequent micromachining processing causes a reduction in pressureof fluid 24 such that the “final” pressure of fluid 24 provides theselected, designed or predetermined mechanical damping of micromachinedmechanical structure 12.

[0086] It should be noted that, in these embodiments, it may beadvantageous to employ a metal bearing material (for example, silicides)to form encapsulation layer 26 c (FIG. 8A) and encapsulation layer 26 d(FIG. 8B). The encapsulation layer 26 c (FIG. 8A) and encapsulationlayer 26 d (FIG. 8B) may be, for example deposited, formed or grownusing, for example, an epitaxial, a sputtering or a CVD-based reactor(for example, APCVD).

[0087] In another aspect of the present invention, the MEMS may includea plurality of monolithically integrated micromachined mechanicalstructures having one or more electromechanical systems (for example,gyroscopes, resonators, temperature sensors and/or accelerometers). Themicromachined mechanical structures may include mechanical structuresthat are disposed in a corresponding chamber, which includes anenvironment (i.e., fluid) providing a desired, predetermined,appropriate and/or selected mechanical damping for the mechanicalstructures.

[0088] With reference to FIG. 9, in one embodiment, MEMS 10 includes aplurality of micromachined mechanical structures 12 a-c that aremonolithically integrated on or disposed within substrate 14. Eachmicromachined mechanical structure 12 a-c includes one or moremechanical structures 20 a-p (for the sake of clarity only a portion ofwhich are numbered).

[0089] As described above in detail with respect to FIGS. 3-8C,mechanical structures 20 reside in a respective chamber 24 (for example,mechanical structures 20 a-20 g are disposed in chamber 22 a). Thechamber 22 includes fluid 24, having a selected, desired and/orpredetermined state that is “trapped”, “sealed” and/or contained withinchamber 22. The fluid 24 provides a desired, predetermined, appropriateand/or selected mechanical damping for mechanical structures 20 a-d.

[0090] In certain embodiments, fluids 24 a-d are “trapped” and “sealed”in chambers 22 a-d, as described above, and maintained and/or containedat the same or substantially the same selected, desired and/orpredetermined state. As such, in these embodiments, fluids 24 a-d mayprovide the same or substantially the same desired, predetermined,appropriate and/or selected mechanical damping for mechanical structures20 a-p.

[0091] In other embodiments, fluids 24 a-d are “trapped”, “sealed”,maintained and/or contained in chambers 22 a-d, as described above, toprovide differing or different mechanical damping characteristics formechanical structures 20 a-p. In this way, structure 12 a may include,for example, a resonator (requiring a Q of, for example, 10,000) andstructure 12 d may include, for example, an accelerometer (requiring a Qof, for example, 0.6). Accordingly, fluids 24 a-d may providesubstantially different desired, predetermined, appropriate and/orselected mechanical damping for mechanical structures 20 a-p.

[0092] Indeed, in at least one embodiment, structure 12 c includes aplurality of chambers, namely chambers 22 c and 22 d, each containingfluid 24 c and 24 d, respectively. The fluids 24 c and 24 d may be“trapped”, “sealed”, maintained and/or contained in chambers 22 c and 22d, respectively, at the same or substantially the same selected, desiredand/or predetermined states. As such, in this embodiment, fluids 24 cand 24 d may provide the same or substantially the same desired,predetermined, appropriate and/or selected mechanical damping formechanical structures 20 h-k and 20 l-p, respectively.

[0093] Alternatively, in at least another embodiment, fluids 24 c and 24d may be “trapped”, “sealed”, maintained and/or contained in chambers 22c and 22 d, respectively, at different or substantially differentselected, desired and/or predetermined states. In this embodiment,chambers 22 c and 22 d may be “sealed” using different processingtechniques, different processing conditions and/or different materials(for example, gases or gas vapors). As such, after encapsulation, fluids24 c and 24 d provide different or substantially different mechanicaldamping characteristics for mechanical structures 20 h-k and 20 l-p,respectively. In this way, micromachined mechanical structure 12 c mayinclude different electromechanical systems (for example, gyroscopes,resonators, temperature sensors and accelerometers) that requiredifferent or substantially different mechanical damping characteristicsfor optimum, predetermined, desired operation.

[0094] It should be noted that in the embodiment illustrated in FIG. 9,micromachined mechanical structures 12 a-c may include the samefeatures, attributes, alternatives, materials and advantages, as well asbe fabricated in the same manner, as the mechanical structure 12illustrated in FIGS. 1-8C, and described above. For the sake of brevity,those features, attributes, alternatives, materials, techniques andadvantages will not be restated here.

[0095] Moreover, the discussion above with respect to fluid 24 and/orfluid 24 in conjunction with FIGS. 3-8C is entirely, fully andcompletely applicable to these sets of embodiments. For the sake ofbrevity, it will not be repeated.

[0096] It should be further noted that the features, attributes,alternatives, materials and advantages, as well as the fabricationtechniques, of the embodiment illustrated in FIG. 9 (and describedabove) are fully and equally applicable to MEMS illustrated in FIGS.1-8C. For example, micromachined mechanical structure 12 of FIG. 3 mayinclude a plurality of chambers to maintain and/or contain fluids at thesame, substantially the same, different or substantially differentselected, desired and/or predetermined states (for example,micromachined mechanical structure 12 c of FIG. 9). Accordingly, thefluids in the chambers may provide the same, substantially the same,different or substantially different mechanical damping characteristicsfor mechanical structures (for example, fluids 24 c and 24 d which are“trapped”, “sealed”, maintained and/or contained in chambers 22 c and 22d of micromachined mechanical structure 12 c of FIG. 9). For the sake ofbrevity, those features, attributes, alternatives, materials, techniquesand advantages will not be restated here. There are many inventionsdescribed and illustrated herein. While certain embodiments, features,materials, configurations, attributes and advantages of the inventionshave been described and illustrated, it should be understood that manyother, as well as different and/or similar embodiments, features,materials, configurations, attributes, structures and advantages of thepresent inventions that are apparent from the description, illustrationand claims. As such, the embodiments, features, materials,configurations, attributes, structures and advantages of the inventionsdescribed and illustrated herein are not exhaustive and it should beunderstood that such other, similar, as well as different, embodiments,features, materials, configurations, attributes, structures andadvantages of the present inventions are within the scope of the presentinvention.

[0097] For example, it may be advantageous to employ gas species thatare compatible with the standard type reactors. In this way, anymodifications or customizations of the reactors to, for example, form,grow or deposit second encapsulation layer 26 b, may be minimized and/oreliminated.

[0098] Further, it may be advantageous to employ gas species that arerelatively inexpensive and available to the reactor/fabricationfacility. In this way, the costs of MEMS 10 may be minimized and/orreduced.

[0099] The term “depositing” means, among other things, depositing,creating, forming and/or growing a layer of material using, for example,a reactor (for example, an epitaxial, a sputtering or a CVD-basedreactor (for example, APCVD, LPCVD, or PECVD)).

[0100] Finally, it should be further noted that while the presentinventions have been described in the context of microelectromechanicalsystems including micromechanical structures or elements, the presentinventions are not limited in this regard. Rather, the inventionsdescribed herein are applicable to other electromechanical systemsincluding, for example, nanoelectromechanical systems. Thus, the presentinventions are pertinent to electromechanical systems, for example,gyroscopes, resonators, temperatures sensors and/or accelerometers, madein accordance with fabrication techniques, such as lithographic andother precision fabrication techniques, which reduce mechanicalcomponents to a scale that is generally comparable to microelectronics.

What is claimed is:
 1. A method of sealing a chamber of anelectromechanical device having a mechanical structure, wherein themechanical structure is in the chamber and wherein the chamber includesa fluid that is capable of providing mechanical damping for themechanical structure, the method comprising: depositing a sacrificiallayer over at least a portion of the mechanical structure; depositing afirst encapsulation layer over the sacrificial layer; forming at leastone vent through the encapsulation layer to expose at least a portion ofthe sacrificial layer; removing at least a portion of the sacrificiallayer to thereby form the chamber; introducing at least one relativelystable gas into the chamber; and depositing a second encapsulation layerover or in the vent to thereby seal the chamber wherein the fluid withinthe chamber includes the relatively stable gas.
 2. The method of claim 1wherein the at least one relatively stable gas is helium, nitrogen,neon, argon, krypton, xenon or perfluorinated hydrofluorocarbons.
 3. Themethod of claim 2 wherein the electromechanical device is amicroelectromechanical device.
 4. The method of claim 2 wherein theelectromechanical device is a nanoelectromechanical device.
 5. Themethod of claim 1 wherein the second encapsulation layer includes asilicon-bearing compound.
 6. The method of claim 5 wherein thesilicon-bearing compound is at least one of monocrystalline silicon,polycrystalline silicon, silicon dioxide, or silicon carbide, BPSG, PSGor silicon nitride.
 7. The method of claim 1 wherein depositing a secondencapsulation layer includes using an epitaxial or a CVD reactor.
 8. Themethod of claim 1 wherein the relatively stable gas includes a lowdiffusivity.
 9. The method of claim 1 further including heating thefluid in, or diffusing a gas into, the chamber to adjust the pressure ofthe fluid to be within a predetermined range of pressures.
 10. Themethod of claim 1 wherein the electromechanical device is anaccelerometer and the pressure of the fluid in the chamber issufficiently high to provide sufficient mechanical damping for themechanical structure.
 11. A method of sealing a chamber of anelectromechanical device having a mechanical structure, wherein themechanical structure resides in the chamber and wherein the chamberincludes a fluid having a pressure that provides mechanical damping forthe mechanical structure, the method comprising: depositing a firstencapsulation layer over the mechanical structure; forming at least onevent through the encapsulation layer; forming the chamber; depositing asecond encapsulation layer by introducing at least one gaseousdeposition reagent into an epitaxial or a CVD reactor to thereby form asecond encapsulation layer over or in the vent to thereby seal thechamber; and wherein the fluid within the chamber includes at least oneby-product resulting from depositing a second encapsulation layer andwherein the pressure of the fluid is sufficient to provide apredetermined mechanical damping for the mechanical structure.
 12. Themethod of claim 11 wherein the at least one by-product includes a lowdiffusivity.
 13. The method of claim 11 wherein the electromechanicaldevice is a microelectromechanical device or a nanoelectromechanicaldevice.
 14. The method of claim 13 further including: introducing atleast one relatively stable gas into the chamber while depositing thesecond encapsulation layer.
 15. The method of claim 14 wherein the atleast one relatively stable gas is helium, nitrogen, neon, argon,krypton, xenon or perfluorinated hydrofluorocarbons.
 16. The method ofclaim 15 wherein the second encapsulation layer includes asilicon-bearing compound.
 17. The method of claim 16 wherein thesilicon-bearing compound is polycrystalline silicon.
 18. The method ofclaim 16 wherein the silicon-bearing compound is at least one of silicondioxide, BPSG, PSG, silicon nitride, or silicon carbide.
 19. The methodof claim 11 wherein further including heating the fluid in, or diffusinga gas into, the chamber to adjust the pressure of the fluid to be withina predetermined range of pressures.
 20. The method of claim 11 whereinthe electromechanical device is an accelerometer and the pressure of thefluid in the chamber is sufficiently high to provide sufficientmechanical damping for the mechanical structure.
 21. Anelectromechanical device comprising: a chamber including a firstencapsulation layer having at least one vent; a mechanical structure,wherein the mechanical structure is disposed in the chamber; a secondencapsulation layer, deposited over or in the vent, to thereby seal thechamber wherein the chamber includes at least one relatively stable gas.22. The electromechanical device of claim 21 wherein the secondencapsulation layer is deposited using an epitaxial, a sputtering or aCVD reactor.
 23. The electromechanical device of claim 22 wherein thefirst encapsulation layer is deposited using an epitaxial, a sputteringor a CVD reactor.
 24. The electromechanical device of claim 21 whereinthe at least one relatively stable gas is helium, nitrogen, neon, argon,krypton, xenon or perfluorinated hydrofluorocarbons.
 25. Theelectromechanical device of claim 21 wherein the second encapsulationlayer is a silicon-bearing compound.
 26. The electromechanical device ofclaim 25 wherein the silicon-bearing compound is at least one ofmonocrystalline silicon, polycrystalline silicon, silicon dioxide, BPSG,PSG, silicon nitride, or silicon carbide.
 27. The electromechanicaldevice of claim 25 wherein the second encapsulation layer is a metalbearing material.
 28. The electromechanical device of claim 27 whereinthe metal bearing material is a silicide.
 29. The electromechanicaldevice of claim 21 wherein the relatively stable gas has a lowdiffusivity.
 30. The electromechanical device of claim 21 furtherincluding a third encapsulation layer, disposed over the secondencapsulation layer, to reduce the diffusion of the fluid from thechamber.
 31. The electromechanical device of claim 30 wherein the thirdencapsulation layer is a metal bearing material.
 32. Theelectromechanical device of claim 31 wherein the metal bearing materialis deposited using an epitaxial, a sputtering or a CVD reactor.
 33. Theelectromechanical device of claim 30 wherein the third encapsulationlayer is at least one of monocrystalline silicon, polycrystallinesilicon, silicon dioxide, BPSG, PSG, silicon nitride or silicon carbide.34. The electromechanical device of claim 21 further including a thirdencapsulation layer, disposed over the second encapsulation layer, toreduce the diffusion of the fluid from the chamber wherein the fluidincludes helium, neon or hydrogen that was diffused through the secondencapsulation layer and into the chamber to adjust the pressure of thefluid to be within a predetermined range of pressures.
 35. Theelectromechanical device of claim 34 wherein the third encapsulationlayer is a metal bearing material.